Traditional techniques for estimating sequences of data symbols transmitted over unknown, fast fading channels have used sequential processing across the many symbols in a given sequence. That is, all of the symbols are processed in the order they are received in order to estimate the entire sequence. Estimation is necessary because the exact sequence of symbols is unknown. This sequential technique is subject to inaccuracies, however.
Accordingly, it is an object of the present invention to provide for methods and devices which allow for the accurate estimation of QAM symbol sequences over flat-fading channels.
It is another object of the invention to provide for methods and devices which improve the estimation of QAM symbol sequences over flat-fading channels by providing for reduced bit error rates.
It is yet a further object of the present invention to provide for methods and devices which improve the estimation of QAM symbol sequences over flat-fading channels by separating a received QAM sequence of data symbols into multiple, separate sequences of symbols, each separate sequence being offset in time, and generating an estimate of the sequence of symbols and fading process for each separated sequence.
Other objectives, features and advantages of the present invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings.
In accordance with the present invention there are provided methods and devices for splitting a received sequence of QAM data symbols into multiple, preferably non-overlapping, sequences. Once the multiple sequences have been created, estimations are then generated independently for each of these multiple sequences. The results of these independent estimation processes are then combined and a final estimation of a fading process is generated. From this estimation the state of each unknown symbol can be determined. One type of QAM signal is an M-Phase-Shift Keying (xe2x80x9cM-PSKxe2x80x9d) signal. Reduced bit error rates have been achieved for sequences of 8-PSK data symbols due to the increased diversity from the use of multiple estimators. Degradation in the estimation process caused by phase ambiguities is also reduced. The present invention is directed at flat-fading, low-dispersion channel and is not directly applicable to frequency-selective, fading environments.
The present invention and its advantages can be best understood with reference to the drawings, detailed description of the preferred embodiments and claims that follow.